Now that more and more of the Civil guys are stating to use some of the MAP tools in Civil 3D and going out there on the wide open web looking for data I think its time to explain (as best as I can) what metadata is. First off anyone that downloads files from the Internet knows they may not get what that download link is “LABELED” as. But most download links at the GeoComm and GISUser sites or sites listed on there are pretty safe as far as being data instead of spy ware or a virus. With that said let me tell everyone that doesn’t know what metadata is.
Metadata or to be more precise Spatial Metadata is the info on the data. The who, what, where, how, and why of the data. Most download sites will have an “Info”or “Metadata” button next to the “Download” button that will bring up the metadata in some form or another. This insures that you download what you want. No site administrator wants you downloading 15M of info to find out you don’t want it and have to download another 15M of data, so most sites are good about providing the metadata before you download.
Metadata files are broken out into a number of different sections or categories, there is a standard both Federal and ISO but not everyone follows it or it was not in place when that medatdata was written so beware when you read it, you may have to really look for the info you need in the file.
One of the first sections is the Identification Section. This area contains the description of the data, the time frame that the data covers, the status of the data, the spatial area or bounding coordinates it covers, any restrictions on using the data, the point of contact for the dataset, and the environment that the data was created in( ex: ESRI running in Windows 3.1 or MurphMap running on a Uni graph system).
Data Quality, this section gets into how accurate is the data. If points were GPSed and what the settings where at the time of the location, did the data entry clerk use spell checker when they filled in the data? Did they trace over raster scan images to create the geometry, what was the cloud over when the plane flew over to snap those aerials photos. The Spatial data and references sections will tell you what the type of object the data is, raster, points polygons or lines. It also will list the coordinates system to include the projection the data is in.
Another useful bit of info is in the Entity and Attribute section , here you will find a detail description of the objects and their attributes. It’s nice to know if a field name STR is for street or stream before you start to theme the data. Other info in this section may be the time frame for those field values and the accuracy of the values.
The Distribution section contains the info on how to get the info (if it’s not available on line) and where to send the check to. <— Just checking to see if you are still reading this. this section also lists any rules on passing the info on to others and may include the disclaimers. The next section is called the Metadata section and included the data on the data on the data. OK I made that part up but there is a section on explaining who wrote the metadata and when it was created, so if you cannot make heads or tails out of it there should be a point of contact to complain to. One of the last sections is the contact section, this is the part that lists everyone and what department created the datasets and how you can contact them for more or to clarify any questions.
So as you can see there is a lot of info that can be part of a data set when you use the metadat files. Just be cautious of when it was created and the style that it may be laid out. Not all of it is the same format and it may take some digging to find that info that explains what you are downloading.